1.) Field of the Invention
The present invention relates to aromatic polyetherketone resin compositions having excellent heat resistance, fiber-reinforced resin compositions obtained by adding carbon fibers to the resin compositions, and mechanical components made of the fiber-reinforced resin compositions and suitable for use in internal combustion engines or auxiliary equipment, especially impellers for centrifugal compressors, power transmitting gears, and the like.
2.) Description of the Related Art
Aromatic polyetherketone resins are expected to find utility in electric and electronic equipment, machinery, automobiles and the like, because they are engineering plastics excellent in mechanical, chemical and thermal properties.
With the recent advances of technology, there is an increasing demand for materials having, at enhanced levels, the characteristics of aromatic polyetherketone resins, especially their heat resistance. It has hence been the practice that a fibrous reinforcing material such as glass fibers or carbon fibers is incorporated in aromatic polyetherketone resins to improve both mechanical strength and heat resistance.
The above conventional practice is however accompanied by the drawback that the mechanical strength at high temperatures can be improved but the reduction of strength in a temperature range around the glass transition temperature of the matrix remains unimproved.
The following problems also arise when carbon fibers are incorporated as a reinforcing material in aromatic polyetherketone resins.
Carbon fibers are widely employed to reinforce plastic materials whose matrix resins are epoxy resins. Epoxy resins are therefore used as binders for carbon fibers. Such epoxy resin binders are effective where thermosetting resins such as epoxy resins are used as matrix resins, but have poor adhesion to thermoplastic resins such as aromatic polyetherketone resins so that the epoxy resin binders cannot provide resin compositions having good mechanical strength. It has hence been attempted to use polyamide resins as binders for thermoplastic resins as disclosed in Japanese Patent Application Laid-Open No. 106752/1978. A high temperature of at least 370.degree. C. is however required to mold or otherwise form aromatic polyetherketone resins. When carbon fibers bound with an epoxy resin or polyamide resin are used, the binder may undergo thermal decomposition during the molding, thereby causing problems such as the formation of voids and strength reduction at welded portions.
On the other hand, Japanese Patent Application Laid-Open No. 120730/1981 discloses the use of carbon fibers bound with an aromatic polysulfone resin. The aromatic polysulfone resin is said to overcome the problems such as the formation of voids and strength reduction at welded portions. The improvement in mechanical strength is however small, so that there is an outstanding demand for a still greater improvement in mechanical strength. Further, in an aromatic polyetherketone resin composition containing carbon fibers bound with an aromatic polysulfone resin, the aromatic polysulfone resin is present at the interfaces between the carbon fibers and the aromatic polyetherketone resin. It has therefore been pointed out that the mechanical strength of this resin composition is lowered when it is dipped in a chemical solution which attacks the aromatic polysulfone resin.
The mechanical strength of the aromatic polyetherketone resin can be improved by the incorporation of carbon fibers. This method is however accompanied by the drawback that its strength reduction in the temperature range above the glass transition temperature of the matrix cannot be improved.
Exemplary conventional impellers made of a fiber-reinforced resin include those disclosed in Japanese Patent Publication No. 48684/1977 and Japanese Patent Application Laid-Open Nos. 135132/1982, 119105/1982, 18296/1984 and 283797/1986. The resin materials which make up these impellers feature the use of carbon fibers as a reinforcing material for the resins. In particular, Japanese Patent Application Laid-Open No. 119105/1982 discloses that carbon-fiber-reinforced resins comprising heat-resistant thermoplastic resins or thermo-setting resins as matrix resins can be used in impellers.
The impeller of a centrifugal compressor is however used under such conditions that the temperature ranges from -50.degree. C. to 200.degree. C. (maximum temperature during ordinary application: 165.degree. C.) and the maximum revolution speed reaches as high as 13.times.104 rpm. Moreover, the stress which occurs when driven at the highest revolution speed reaches about 20 kg/mm.sup.2 in the case of impellers currently used (material: aluminum alloy, outer diameter: about 60 mm). The stress reaches as great as about 10 kg/mm.sup.2 even at the basal part of each blade. The maximum stress at the time of revolution can be reduced about one half or so by using a fiber-reinforced resin whose specific gravity is low. When a material is chosen in view of the currently used conditions while taking into parallel consideration heat resistance, strength (tensile, flexural and compression), modulus of elasticity (tensile and flexural), durability, fatigue resistance (tensile and flexural), and creep characteristics, the thermoplastic resins and thermosetting resins disclosed in Japanese Patent Application Laid-Open No. 119105/1982 can by no means be used as they are.
As fiber-reinforced resin compositions capable of satisfying these conditions, compositions of heat resistant resins--such as polyethersulfones (PES), polyetherimides (PEI), polyetheretherketones (PEEK), polyetherketones (PEK), polyetherketoneketones (PEKK), polyketonesulfides (PKS), polyaryletherketones (PAEK), aromatic polyamides (PA), polyamideimides (PAI), or polyimides (PI)--with carbon fibers, glass fibers, whiskers or the like appear to be promising.
The above-described resins however have a high melting point. It is therefore necessary to mold them by raising the resin-melting temperature to a relatively high temperature of from 350.degree. C. to 430.degree. C. Resin-reinforcing carbon fibers presently available on the market primarily use, as a binder, a polyamide resin (decomposition temperature: 280.degree. C.) for thermoplastic resins or an epoxy resin (decomposition temperature: 300.degree. C.) for thermosetting resins. These binders however involve various problems. Namely, they are susceptible to decomposition at the above-described resin-melting temperature (350.degree. C.-430.degree. C.) upon molding. Due to insufficient wetting of carbon fibers with the matrix resins, the interfacial strength tends to decrease and also to become uneven. When employed as materials for fiber-reinforced-resin-made impellers of centrifugal compressors, they cannot effectively use the reinforcing effect of carbon fibers and have low strength. Further, matrix resins which can exhibit maximum wetting property to carbon fibers when combined with the latter involve the problems that they have a low glass transition temperature and their stiffness is insufficient when used at the maximum temperature of 165.degree. C. which are encountered in the course of ordinary use.